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Dynamics of unsteady compressible cavitating flows associated with the cavity shedding
Ocean Engineering ( IF 5 ) Pub Date : 2020-08-01 , DOI: 10.1016/j.oceaneng.2020.107025
Changchang Wang , Guoyu Wang , Biao Huang

Abstract The main purpose of this work is to shed light on the physics involved in the two distinct cavity cloud shedding mechanisms in cloud cavitating flows, namely re-entrant jet mechanism (RJM) and shock wave propagation mechanism (SWM). A compressible cavitating flow solver, which considers the compressibility effects of both liquid and vapor, is used to account for the wave dynamics in cavitating flows. The compressible Navier-Stokes equations, coupling the mass, momentum energy equations, and phase fraction transport equation, along with the thermodynamic equations of state for both liquid and vapor, Saito cavitation model and the SST-SAS turbulence model, are solved. Numerical results are presented for the conditions of both the re-entrant jet mechanism and shock wave mechanism around a NACA66 (mod) hydrofoil (Leroux et al., 2005), respectively, with emphasis on the process of re-entrant jet development and shock wave formation and propagation. The results show that the re-entrant jet can cause the attached cavity sheet breakup for both the two cavity cloud shedding mechanisms in both high and low angle of attack, while the shock wave formation and propagation process only occurs under shock wave mechanism at low angles of attack. Pressure evolution illustrates that in the re-entrant jet mechanism, cavity cloud collapse will induce high pressure load, while no shock wave and thus the corresponding rebound phenomenon are observed. In shock wave mechanism, during the whole process of the shock wave dynamics, namely generation, propagation and rebound process, pressure fluctuations increase sharply along with the generation of the pressure peaks with large amplitude and short time interval. Further study on the compressible characteristics involved in the two cavity shedding mechanisms illustrates that vapor fraction and mass transfer have a significant effect in sonic speed and Mach number characteristics. The average and standard derivation of maximum Mach number (Mamax) in shock wave mechanism is lower than that in re-entrant jet mechanism. Cavitating flows are characterized by low sonic speed value in the cavitation region and high sonic speed value in the pure liquid region and a sonic speed boundary layer exists between the two regions, the thickness of which is about the size of the local attached cavity sheet on foil surface. In the process of shock wave generation and rebound, cavity volume and cavity volume rate experience large fluctuations, showing strong cavitation instabilities in shock wave mechanism.

中文翻译:

与空腔脱落相关的非定常可压缩空化流动的动力学

摘要 这项工作的主要目的是阐明云空化流中两种不同的空腔云脱落机制所涉及的物理学,即重入射流机制 (RJM) 和激波传播机制 (SWM)。考虑液体和蒸汽的可压缩性效应的可压缩空化流求解器用于解释空化流中的波动动力学。求解可压缩 Navier-Stokes 方程,耦合质量、动量能量方程和相分数传输方程,以及液体和蒸汽的热力学状态方程、Saito 空化模型和 SST-SAS 湍流模型。针对 NACA66 (mod) 水翼周围的折返射流机制和冲击波机制的条件,给出了数值结果(Leroux 等,2005),分别着重介绍了折返射流的发展和激波的形成和传播过程。结果表明,在高、低攻角两种空腔脱云机制下,再入射流均能引起附着的空腔片破裂,而激波的形成和传播过程仅发生在低迎角的激波机制下。的攻击。压力演化说明在折返射流机制中,空腔云坍塌会引起高压载荷,而没有冲击波,因此观察到相应的回弹现象。在激波机制中,在激波动力学的整个过程,即产生、传播和回弹过程中,随着振幅大、时间间隔短的压力峰值的产生,压力波动急剧增加。对涉及两种腔体脱落机制的可压缩特性的进一步研究表明,蒸汽分数和传质对声速和马赫数特性有显着影响。激波机制中最大马赫数(Mamax)的平均和标准导数低于折返射流机制。空化流的特点是空化区的声速值低,纯液体区的声速值高,两个区域之间存在声速边界层,其厚度约为表面局部附着空腔片的大小。箔表面。在冲击波产生和反弹的过程中,
更新日期:2020-08-01
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